JOEY Prusak, the 19-year-old manager of a Dairy Queen outlet in the United States, has become an online sensation after helping a blind customer who was robbed in his store.

A regular customer of the Dairy Queen, who is visually impaired, ordered a sundae from Mr Prusak on September 10. While paying for the order, he dropped $20 on the floor.

"Right then and there I knew when he dropped that $20 bill, game's over, he's not going to know," Mr Prusak told local TV station KARE 11.

"He just kept walking and that's when the lady picked it up."

An elderly woman swooped on the $20 note and slipped it into her purse.

When she reached the counter, Mr Prusak asked her to return the money. She claimed it was hers.

"I told her I'm not going to serve you if you are going to be disrespectful as you are stealing someone's money like that," Mr Prusak told TheBlaze.

"She started getting really angry ... started swearing and whatnot," he said. "I told her if you aren't going to return the money, you need to leave right now."

The thief stormed out with the blind man's money still in her purse. So Mr Prusak took $20 out of his own wallet and gave it to the man.

Other customers witnessed the incident as they waited in line. One of them wrote a letter to Dairy Queen, praising Mr Prusak's conduct. The letter ended up on Reddit.

"I was in shock by the generosity that your employee had, taking his own money out of his own wallet to give to the customer because some other lady decided to steal something that wasn't hers," the letter reads.

TheBlaze says the store's business has doubled since the incident, and Mr Prusak has received praise from dozens of customers.